This invention pertains to a method and a testing device for testing a container in which a pressure differential is created between a pressure inside the container and a pressure in its environment and from the behavior of one of the pressures, it is established whether the container satisfies predetermined test conditions. The method and testing device are particularly suited to testing the gas tightness of containers.
This invention pertains to a testing device such as is known from U.S. Pat. No. 5,029,464 and EP-A-0 313 678 and EP-A-0 432 143.
From these items a way is known that a pressure differential is to be created between a pressure in the interior of the container and a pressure in said container""s environment in order to test the gas tightness of containers and, from the behavior of one of the pressures, it is to be established whether the container under test satisfies the gas-tightness conditions or volume conditions or not.
In this process the container to be tested is placed in a sealing chamber that is connected to a pressure medium source or a suction source; said arrangement is to be used to create the above-mentioned pressure differential. After the pressure differential is created, a pressure value for the environment of the container in stored as a starting condition in a reference pressure chamber, which is placed in front of a pressure differential sensor, and is compared with subsequent pressure values for the environment of the container.
The above-mentioned documents are thus declared to be an integral part of the present description.
A drawback to the known method is the fact that a pressure differential sensor with extremely accurate control valves must be provided to ensure that even very small leaks or slight deviations of the container volume from a nominal volume are detected.
The goal set for the present invention is to simplify this known method significantly. The method of the invention and the corresponding arrangement as described herein are exceptionally well suited for accomplishing this goal. More particularly, according to the method of the invention for testing containers in which a pressure differential is created between a pressure inside the container and a pressure in its environment and from the behavior of one of the pressures, it is established whether the container satisfies predetermined test conditions, after one of the pressures reaches a predetermined test value or after it has reached a maximum value and said value has been stored, subsequently said pressure is compared for a predetermined time to at least one value of one of the two pressures, in which case at least this one pressure value appears as an output signal of a pressure sensor. The method is especially useful for testing the gas tightness of the containers.
A test arrangement according to the invention for testing containers comprises a pressure or suction source, which can be effectively connected to a container to be tested with respect to its interior and exterior pressure, at least one pressure sensor and a pressure storage arrangement, wherein the pressure sensor is a converter that converts an input-side pressure value into an output-side electrical signal and the output of the sensor, on the one hand, and the output of an electronic pressure-value storage arrangement, on the other, are fed to a comparator unit.
Accordingly, a pressure differential sensor in no longer used, nor are pneumatic storage chambers; instead, the pressure that is of interest in determined by means of a relative-pressure sensor and converted into an electrical signal; when checking for leaks, this signal is stored at a predetermined time and compared with at least one subsequent value that in determined by this same sensor. When checking volume, a pressure value is pre-specified and stored as a basis for comparison. This obviates the need for awkward devices of the previously known type, namely the pressure differential sensor and, in particular, the stop valves that are quite difficult as regards control characteristics.
The method of the invention is implemented in a configuration wherein an electrical output signal of the sensor is compared to one or more predetermined values, e.g., on a computer into which the sensor output is entered. A value of the sensor output signal is stored as a pressure value. Either the pressure in the interior of the container or that in the environment of the container is increased or decreased, and a value of the pressure in the container or in the environment of the container is measured.
The preferable procedure is that both the source connection to admit the pressure medium or to ensure suction and the sensor input are hooked up to either the interior of the container or the container""s environment.
The creation of the pressure differential can be done in different ways, with which the specialist in well acquainted from the above-mentioned documents. Thus, for example, the pressure differential can be created by carrying out pressurization or suction at a predetermined level for a predetermined time, and then analyzing both a pressure value that is reached and its plot. In addition, pressurization can be done to a predetermined pressure differential, and then the plot of the pressure value that is of interest can be observed.
As is known from the above-mentioned documents, pressurization can also be accomplished by precharging a pre-chamber to a predetermined pressure and then discharging said chamber into the container or into an enclosure that is formed by a sealable chamber.
When checking volume, a volume that is dependent on the volume of the container, either the interior volume of said container itself or its volume differential compared to a testing chamber, can be pressurized by a predetermined quantity of pressure medium, or a predetermined amount of gas can be removed from this volume. The volume of the container is then determined from the resulting pressure.
Of course, the values that are measured are compared with nominal values or nominal plots, as is also know from the above-mentioned documents.
Storage, wherein the pressure in the environment of the container is increased or decreased and a value of the pressure of the environment of the container is measured, is preferably undertaken in such a way that, with control at a predetermined time, an analog/digital converter is enabled to convert the sensor output signal, and the then stationary output signal of this analog/digital converter is used as a reference value for the subsequent analysis of the sensor output signal. In this process, either another analog/digital converter can be installed behind the sensor output and the output signal of the latter converter can then be digitally compared to that of the storage unit A/D converter or, preferably, a D/A converter is placed immediately behind the storage ND converter and thus the stored, re-converted signal is fed as an analog reference signal to an analog comparator unit, to which the output signal of the sensor is also fed directly.
In addition, wherein the pressure in the environment of the container is increased or decreased and a value of the pressure of the environment is measured, a null balance is preferably undertaken by determining, essentially during the value storage process at the comparator, whether an output signal of the device encompasses the null value, at least approximately; if a signal appears that deviates from the null value or from a predetermined minimum value, then said signal is used as a null-balance signal.
Preferred embodiments of the test arrangement of the invention for testing containers comprise a pressure or suction source which can be effectively connected to a container to be tested with respect to its interior and exterior pressure, at least one pressure sensor, an electronic pressure-value storage arrangement and a comparator unit. The pressure sensor is a converter that converts an input-side pressure value into an output-side electrical signal. Means are provided for feeding the output of the sensor, on one hand, and the output of the electronic pressure-value storage arrangement, on the other to the comparator unit to commence a measuring test interval at a point in time immediately after the input-side pressure value of the sensor reaches risingly a predetermined test value and rereaches the predetermined test value diminishingly.
The invention is hereinafter explained by way of examples, using figures.